The invention is concerned with time shared numeric display systems. Specifically, the invention is directed to displaying two digit channel numbers on a television receiver. Application Ser. No. 430,446 shows a display system employing separate memories coupled respectively to individual decoders for constantly displaying the information stored in the memories. This invention provides a novel improvement for this and other display systems.
Time sharing of numeric display units is well known in the art. Generally a single decoder is time shared for decoding information to be supplied to the positions in the display device. The positions are illuminated one at a time but fast enough to appear flicker-free. If the time sharing or strobe rate is approximately 50 per second, the eye does not detect any flicker. The advantages of time sharing are that less power is consumed because of non constant operation and a single decoder-driver may be used.
Normally, supplying information to a single decoder is achieved by a multiplexing of the information. In multiplex operations, a series of memories may contain binary coded decimal (BCD) information to be displayed. A clocking system sequentially activates the output terminals of the memories to supply their information to the common decoder which generates decimal information for display. Thus on a time sequenced basis the information for display is multiplexed to the decoder. The clocking system simultaneously selectively activates corresponding display devices thus the information in the various memories is sequentially decoded and supplied to a display device on a regular time sequenced basis at a rate for which the usual display appears to be continuous. The design of the clocking system is usually dictated by the type of display device and the number of digits to be displayed. This invention takes advantage of the AC line frequency, normally supplied to an appliance, to produce clock signals and provide a greatly simplified two digit display system.